Environmentally-friendly vehicles are very important for the future of the motor industry. Vehicle manufacturers are focusing on the development of environmentally-friendly vehicles, such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell electric vehicles (FCEV) so as to meet environmental and fuel consumption regulations.
The vehicle manufacturers have been focusing on gas emission regulations and improving fuel consumption performance restrictions in view of heightened weight and cost, and are competing to commercialize the hybrid electric vehicles.
The hybrid electric vehicles use more than two power sources. Gasoline engines or diesel engines using fossil fuel and motor/generators driven by electrical energy are the two main power sources of hybrid electric vehicles. A the motor/generator having relatively low-speed torque characteristics is used as a main power source at low-speed, and an engine having relatively high-speed torque characteristics is used as a main power source at high-speed.
Since the hybrid electric vehicle stops using fossil fuel and uses the motor/generator when operating the vehicle at a low-speed region, fuel consumption may be improved and exhaust gas may be reduced.
The power transmission system of a hybrid electric vehicle is classified into a single-mode type and a multi-mode type.
According to the single-mode type, even though a torque delivery apparatus such as a clutch and a brake for shifting is not necessary, fuel consumption is high due to deterioration of efficiency at a high-speed region and an additional torque multiplication device is required for a large vehicle.
Because the multi-mode type has high efficiency at the high-speed region and is able to multiply torque autonomously, the multi-mode type can be applied to a full size vehicle. The multi-mode type as the power transmission system of a hybrid electric vehicle is under continuous investigation.
The power transmission system of the multi-mode type includes a plurality of planetary gear sets, a plurality of motor/generators, a plurality of torque delivery apparatus controlling rotation elements of the planetary gear sets, and a battery used as a power source of the motor/generators.
The power transmission system of the multi-mode type has different operating mechanisms depending on connections of the planetary gear sets, the motor/generators, and the torque delivery apparatus.
In addition, the power transmission system of the multi-mode type has different features such as durability, power delivery efficiency, and size depending on the connections of the planetary gear sets, the motor/generators, and the torque delivery apparatus. Therefore, designs for the connection structure of the power transmission system of a hybrid electric vehicle have been under continuous investigation to achieve robust and compact power transmission system having no power loss.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.